The present invention relates to clamping devices and, more particularly, to a spring-loaded clamp for securing a ladder to an over-head or side-mounted rack, especially on a vehicle.
Ladders are one of the most essential pieces of equipment in the building trades. Ladders, however, have always posed a difficult problem with respect to storage and transportation, due to their elongated size. Ladders are usually mounted upon ladder racks that are commonly secured to the sides and roofs of trucks and vans. A typical ladder rack shown in the art is illustrated in the U.S. Pat. No. 4,813,585 issued to Nutt on Mar. 21, 1989 entitled LADDER RACK. The ladder rack of that patent comprises resilient clamps that vertically engage the ladder and pivot into a locking position. The patent eschews the use of biasing means, preferring to employ a slotted keyway and slide pin for locking the clamping arm into position.
One of the disadvantages of using a springless locking mechanism for the clamp is the possibility that harsh jolts, bumps, and travel vibrations will dislodge the securing device. In the event this occurs, the ladder could shift and become dislodged from its mounting rack.
In more recent times, U.S. Pat. No. 5,186,588 issued on Feb. 16, 1993 to Sutton et al entitled LADDER RACK LADDER LATCH discloses a ladder rack and securing mechanism having a spring-loaded latch to secure a clamp about a ladder. The mechanism in that patent has a spring-loaded handle, which pivots and forces the clamping hook to pivotally engage a rung of the ladder.
The problem with the Sutton ladder rack and latch is similar to the aforementioned device taught in the Nutt patent: there is a possibility that the ladder may dislodge when the truck or van traverses rough terrain. Shocks and bumps could conceivably shift the position of the handle, causing the clamp to become undone. This is so because the spring of the device acts directly upon the handle; there is nothing in the mechanism that seems able to prevent the handle from dislodging from its locking position.
The present invention reflects the discovery of an improved spring-loaded clamping device for securing a ladder to a roof or side-mounted ladder rack. The clamping mechanism features a pivot arm that connects to the ladder clamp via a spring, which biases the ladder clamp in a locked position. The clamp of the invention is not subject to dislodgement as are the aforementioned patented devices, by virtue of a pivot arm that travels over top-dead-center in achieving its locked position. Jolts, bumps, and traveling vibrations will not dislodge the pivot arm from its locked position.
In accordance with the present invention, a locking clamp mechanism secures a ladder to a roof or side-mounting rack that may be carried by a vehicle. The locking clamp mechanism comprises a fastener member that attaches to the mounting rack. A handle is pivotally mounted to the fastener member. A curved link is pivotally secured at one end to a mid-portion of the handle. A coiled spring is attached at one of its ends to an opposite end of the curved link. The other end of the spring is attached to a hook member that engages a rung of a ladder. The locking clamp mechanism is operative between an open and locked position in response to the position of the handle, which pivots from an open position over its pivot connection to a locked position. In pivoting, the handle draws the curved link over a top, dead-center position of its pivot, thus securing the hook member in a locked position with respect to said rung of the ladder.
It is an object of this invention to provide an improved clamping mechanism for a ladder that is to be secured to a mounting rack that can be disposed upon a vehicle.
It is another object of the invention to provide a spring-loaded clamping mechanism that locks the clamp holding a ladder to a rack mount by virtue of its linkage, whose motion traverses past the top dead-center of the activating pivot point.